/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.zookeeper.server.quorum;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.net.InetSocketAddress;

import org.apache.jute.BinaryInputArchive;
import org.apache.jute.Record;
import org.apache.zookeeper.server.ObserverBean;
import org.apache.zookeeper.server.Request;
import org.apache.zookeeper.server.util.SerializeUtils;
import org.apache.zookeeper.txn.TxnHeader;

/**
 * Observers are peers that do not take part in the atomic broadcast protocol.
 * Instead, they are informed of successful proposals by the Leader. Observers
 * therefore naturally act as a relay point for publishing the proposal stream
 * and can relieve Followers of some of the connection load. Observers may
 * submit proposals, but do not vote in their acceptance.
 *
 * See ZOOKEEPER-368 for a discussion of this feature.
 */
public class Observer extends Learner {

	Observer(QuorumPeer self, ObserverZooKeeperServer observerZooKeeperServer) {
		this.self = self;
		this.zk = observerZooKeeperServer;
	}

	/**
	 * the main method called by the observer to observe the leader
	 *
	 * @throws InterruptedException
	 */
	void observeLeader() throws InterruptedException {
		zk.registerJMX(new ObserverBean(this, zk), self.jmxLocalPeerBean);

		try {
			InetSocketAddress addr = findLeader();
			LOG.info("Observing " + addr);
			try {
				connectToLeader(addr);
				long newLeaderZxid = registerWithLeader(Leader.OBSERVERINFO);

				syncWithLeader(newLeaderZxid);
				QuorumPacket qp = new QuorumPacket();
				while (self.isRunning()) {
					readPacket(qp);
					processPacket(qp);
				}
			} catch (IOException e) {
				LOG.warn("Exception when observing the leader", e);
				try {
					sock.close();
				} catch (IOException e1) {
					e1.printStackTrace();
				}

				// clear pending revalidations
				pendingRevalidations.clear();
			}
		} finally {
			zk.unregisterJMX(this);
		}
	}

	/**
	 * Controls the response of an observer to the receipt of a quorumpacket
	 * 
	 * @param qp
	 * @throws IOException
	 */
	protected void processPacket(QuorumPacket qp) throws IOException {
		switch (qp.getType()) {
		case Leader.PING:
			ping(qp);
			break;
		case Leader.PROPOSAL:
			LOG.warn("Ignoring proposal");
			break;
		case Leader.COMMIT:
			LOG.warn("Ignoring commit");
			break;
		case Leader.UPTODATE:
			LOG.error("Received an UPTODATE message after Observer started");
			break;
		case Leader.REVALIDATE:
			revalidate(qp);
			break;
		case Leader.SYNC:
			((ObserverZooKeeperServer) zk).sync();
			break;
		case Leader.INFORM:
			TxnHeader hdr = new TxnHeader();
			Record txn = SerializeUtils.deserializeTxn(qp.getData(), hdr);
			Request request = new Request(null, hdr.getClientId(), hdr.getCxid(), hdr.getType(), null, null);
			request.txn = txn;
			request.hdr = hdr;
			ObserverZooKeeperServer obs = (ObserverZooKeeperServer) zk;
			obs.commitRequest(request);
			break;
		}
	}

	/**
	 * Shutdown the Observer.
	 */
	public void shutdown() {
		LOG.info("shutdown called", new Exception("shutdown Observer"));
		super.shutdown();
	}

	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder();
		sb.append("Observer ").append(sock);
		sb.append(" pendingRevalidationCount:").append(pendingRevalidations.size());
		return sb.toString();
	}
}
